Upstream update af3bb68add1c40d19d0dee382009e21b0870a38f

Author: NRK <nrk@disroot.org>
    Date:   Fri Mar 18 16:20:54 2022 +0600

    avoid potential UB when using isprint()

    all the ctype.h functions' argument must be representable as an unsigned
    char or as EOF, otherwise the behavior is undefined.

st/st.c

@@ -422,7 +422,7 @@ static const char base64_digits[] = {
 char
 base64dec_getc(const char **src)
 {
-	while (**src && !isprint(**src))
+	while (**src && !isprint((unsigned char)**src))
 		(*src)++;
 	return **src ? *((*src)++) : '=';  /* emulate padding if string ends */
 }